Carotenoids are natural pigments useful as feed additives, food additives, drugs, and the like. Examples of carotenoids include zeaxanthin, β-carotene, β-cryptoxanthin, astaxanthin, canthaxanthin, lycopene, phoenicoxanthin, adonixanthin, echinenone, asteroidenone, and 3-hydroxyechinenone.
Among carotenoids, zeaxanthin is added to feedstuffs as a natural yellow pigment contained in various plants such as corn. Known applications thereof include the improvement of the color tone of the egg yolk, meat, epidermis of poultry such as chickens, and food colorants. Moreover, zeaxanthin has a strong anti-oxidizing effect, and thus it has been revealed to play an important role in human eye health (Non-Patent Document 1). There is a high level of zeaxanthin in the macular region (central part) of the retina. It is considered to exhibit functions for filtering harmful light such as ultraviolet rays and to exhibit the functions of an antioxidant.
Based on these physiological effects, zeaxanthin is considered to be involved in overall eye health and, in particular, the risk of eye diseases such as Age-related Macular Degeneration (AMD) (Non-Patent Document 2). Other effects thereof that have been reported are anti-tumor effects (Non-Patent Document 3). Hence, zeaxanthin is considered to be a promising material for health foods and drugs.
Zeaxanthin kinetics in the human body when it is used for such applications are examined as follows. It is said that a human incorporates zeaxanthin into the body via the intestinal tract after intake of zeaxanthin orally from material consumed during a diet. Human in vivo kinetics of zeaxanthin incorporated into the human body are mediated by blood. Actually, human blood already contains zeaxanthin from a normal diet (Non-Patent Document 4). Furthermore, many attempts to increase human blood zeaxanthin concentration have been reported to date. Possible zeaxanthin sources are plant-based zeaxanthin sources including vegetables such as spinach and corn and citrus fruits such as oranges, animal-based zeaxanthin sources including chicken egg yolk, or supplements containing zeaxanthin. Of these sources, the concentrations of plant-based zeaxanthin sources cannot be easily increased in an artificial manner. Hence, methods for increasing such zeaxanthin concentrations are classified roughly into the following two categories: methods for increasing the concentration of zeaxanthin in chicken eggs by incorporating a zeaxanthin source into feedstuffs for chickens and methods for increasing human blood zeaxanthin levels using supplements.
As methods for producing zeaxanthin, a chemical synthesis method that involves using as a raw material optically active hydroxy ketone obtained by asymmetric reduction of oxoisophorone (Non-Patent Document 5) and a method that involves extracting it from corn seeds (Non-Patent Document 6) are known, for example. Furthermore, a method that involves extracting zeaxanthin from marigold is also known (Patent Document 1), however, a major ingredient of marigold-derived carotenoid is lutein and the zeaxanthin content is low.
Moreover, known examples of microorganisms producing zeaxanthin include spirulina algae (Patent Document 2), microalgae of the genus Nannochloris (Patent Document 3), bacteria of the genus Flexibacter (Patent Document 4), bacteria of the genus Alteromonas (Patent Document 5), bacteria of the genus Flavobacterium (Non-Patent Document 7), and Agrobacterium aurantiacum bacteria (Non-Patent Document 8). Furthermore, from among bacteria of the genus Paracoccus known as carotenoid-producing bacteria, Paracoccus zeaxanthinifaciens ATCC 21588 strain (Non-Patent Document 9), a mutant strain of Paracoccus carotinifaciens E-396 bacterial strain (Patent Document 6), a mutant strain of A-581-1 bacterial strain of the genus Paracoccus (Patent Document 6), and a mutant strain of bacteria of the genus Paracoccus (Patent Document 7) are known to produce zeaxanthin, for example.
An example of administration of zeaxanthin as a supplement to a human is the use of such a supplement obtained from industrial culture of Flavobacteria (Non-Patent Document 10). In such a case, when 30 mg of the supplement was taken every day for 120 days, the initial blood zeaxanthin concentration of 0.086 μM increased to 0.48 μM. In this case, the proportion of the increase to the intake was 0.01 μM/(mg/Day) (“μM/(mg/Day)” refers to the increase in the blood zeaxanthin concentration (μM) divided by the zeaxanthin intake per day (mg/Day)). In an example of administration of chemically synthesized zeaxanthin to a human (Non-Patent Document 11), when 12.6 mg of chemically synthesized zeaxanthin was taken every day for 6 months, the initial blood zeaxanthin concentration of 0.04 μM increased to 0.85 μM. In this case, the proportion of the increase to the intake was 0.06 μM/(mg/Day). Subsequently, when zeaxanthin in an amount twice the amount of the initial dose was further taken for 6 months, blood zeaxanthin concentration increased to 1.09 μM. In this case, the proportion of the increase to the intake was 0.01 μM/(mg/Day).
In contrast to these cases of administration of the supplements, several cases of increases in human blood zeaxanthin concentrations upon consumption of chicken eggs have been reported. When 2 chicken eggs/day or 4 chicken eggs/day were consumed for 35 days (Non-Patent Document 12), while the blood zeaxanthin concentration before consumption was 0.03 μM, the concentration increased to 0.05 μM and 0.06 μM, respectively. In this case, the proportion of the increase to the consumption was 0.03 μM/(mg/Day). Moreover, when 1 chicken egg/day was consumed for 35 days (Non-Patent Document 13), while the blood concentration before consumption was 0.04 μM, the blood concentration after consumption was 0.06 μM, and the proportion of the increase to the consumption (intake) was 0.16 μM/(mg/Day). When 6 chicken eggs/week were consumed for 12 weeks (Non-Patent Document 14), while the blood concentration before consumption was 0.1 μM, the blood concentration after consumption was 0.15 μM, and the proportion of the increase to the consumption (intake) was 0.43 μM/(mg/Day).
Taken together, the intake of zeaxanthin can be relatively easily increased in the above examples involving supplements, and thus human blood zeaxanthin concentration can be increased (0.48 μM to 1.09 μM). However, the effect of the intake on blood zeaxanthin concentration is very low, so that high intake thereof is required. In general, the production cost for carotenoids is very high, and thus such low efficiency is problematic.
Meanwhile, the number of chicken eggs that can be consumed per day is no higher than 1 to 2 chicken eggs per day, because of concern about cholesterol and the like. Therefore, the human blood zeaxanthin concentration that can be expected therefrom is very low (0.06 μM to 0.15 μM). However, in view of efficiency, the efficiency in the case of chicken eggs is higher than that in the case of supplements. Therefore, if a large amount of zeaxanthin can be introduced into a chicken egg, human blood zeaxanthin concentration can be increased easily and effectively.
In the recent chicken egg market, apart from general eggs obtained by feeding chickens with general feedstuffs, high-value added special eggs can be obtained by feeding chickens with a feedstuff supplemented with a functional ingredient such as folic acid (Patent Document 8), vitamin E (Patent Document 9), linseed (Patent Document 10), or astaxanthin (Patent Document 11).
As methods for increasing zeaxanthin concentration in egg yolk with the use of a feedstuff containing zeaxanthin, a method that involves adding spirulina alga body to a feedstuff (Patent Document 2), a method that involves adding Chinese wolfberry fruit or an extract thereof to a feedstuff (Patent Document 12), and the like are known.
However, production of high-concentration zeaxanthin-enriched eggs by adding spirulina to a feedstuff is problematic in that a large amount of spirulina must be added, since the zeaxanthin concentration in the spirulina alga body is low (1.0 mg/g). It is desirable that the amount added be as low as possible in order to keep the nutritional balance in the feedstuff. When zeaxanthin concentration has been enriched using spirulina, the zeaxanthin concentration in chicken egg yolk has been no higher than 1.65 mg/100 g.
Meanwhile, the addition of Chinese wolfberry fruit to a feedstuff has drawbacks such that, in addition to low zeaxanthin concentration in Chinese wolfberry fruit (1.1 mg/100 g), stable supplies thereof are difficult to attain, since the growth thereof is affected by weather. Furthermore, the zeaxanthin concentration in chicken egg yolk with a zeaxanthin concentration enriched using Chinese wolfberry fruit has been no higher than 3.35 mg/100 g.
Therefore, the following methods have been required: a method for producing chicken eggs using a raw material having a high zeaxanthin concentration, which allows the amount of the raw material necessary to add to a feedstuff to be low, and enables enrichment of the zeaxanthin concentration in chicken egg yolk to 3.35 mg/100 g or more and a stable supply of chicken eggs; and a method for efficiently increasing the human blood zeaxanthin level using such chicken eggs.